Employee Benefit Plans (Summary of Activity in Corporation's Active Stock Plans) (Detail) - $ / shares	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, number of shares	(399,224)	(548,238)	(1,150,920)
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	55,370	48,910	53,008
Beginning balance, number of shares/units	48,910	53,008	53,659
Ending balance, weighted-average grant-date fair value	$ 74.76	$ 71.14	$ 64.87
Beginning balance, weighted-average grant-date fair value	$ 71.14	$ 64.87	$ 61.48
Granted in period, number of shares/units	7,592	6,576	5,447
Granted in period, weighted-average grant-date fair value	$ 102.70	$ 109.58	$ 95.37
Stock awards exercised/vested in period, number of shares	(1,132)	(10,674)	(6,098)
Stock awards exercised/vested in period, weighted-average grant date fair value	$ 106.03	$ 63.68	$ 62.29
Non-Vested Stock Awards/ Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	440,647	383,797	312,656
Beginning balance, number of shares/units	383,797	312,656	256,850
Ending balance, weighted-average grant-date fair value	$ 90.22	$ 85.59	$ 81.71
Beginning balance, weighted-average grant-date fair value	$ 85.59	$ 81.71	$ 73.43
Granted in period, number of shares/units	127,091	109,847	99,833
Granted in period, weighted-average grant-date fair value	$ 93.46	$ 94.81	$ 98.90
Stock awards exercised/vested in period, number of shares	(53,990)	(32,050)	(39,740)
Stock awards exercised/vested in period, weighted-average grant date fair value	$ 65.11	$ 78.92	$ 71.59
Forfeited/expired in period, number of shares/units	(16,251)	(6,656)	(4,287)
Forfeited/expired in period, weighted-average grant date fair value	$ 89.71	$ 87.60	$ 79.52
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted in period, number of shares/units	34,317	30,466	24,162
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares	1,980,866	2,352,008	2,917,142
Beginning balance, number of shares	2,352,008	2,917,142	4,089,028
Ending balance, weighted-average exercise price	$ 64.60	$ 63.55	$ 63.34
Beginning balance, weighted-average exercise price	$ 63.55	$ 63.34	$ 62.67
Stock options exercised, number of shares	(359,892)	(513,134)	(1,118,122)
Stock options exercised, weighted-average exercise price	$ 57.71	$ 61.68	$ 60.59
Forfeited/expired, number of shares	(11,250)	(52,000)	(53,764)
Forfeited/expired, weighted-average exercise price	$ 65.11	$ 70.42	$ 69.78
Maximum [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	177,288	125,809	80,106
Beginning balance, number of shares/units	125,809	80,106	43,860
Ending balance, weighted-average grant-date fair value	$ 83.48	$ 82.55	$ 79.91
Beginning balance, weighted-average grant-date fair value	$ 82.55	$ 79.91	$ 69.70
Granted in period, number of shares/units	51,479	45,703	36,246
Granted in period, weighted-average grant-date fair value	$ 85.74	$ 87.18	$ 92.27

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Number of share options (or share units) exercised during the current period.

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